THE STRUCTURE AND DEVELOPMENT OF THE RAT RETINA - AN IMMUNOFLUORESCENCE MICROSCOPICAL STUDY USING ANTIBODIES SPECIFIC FOR INTERMEDIATE FILAMENT PROTEINS

Abstract

Rat retina structure was studied between embryonic day 14 and adult with antibodies specific for vimentin, glial fibrillary acid protein (GFA) and the proteins of the neurofilament triplet. Vimentin could be detected in radial processes throughout the retina at all stages studied. These processes are believed to correspond, in the developing retina, to ventriculocytes, and in the mature retina to Mueller cells. They could not normally be stained with any of the other intermediate filament antibodies employed here. Some older albino rats possessed GFA staining in addition to vimentin in these processes. Since such staining was never seen in the retinae of mature non-albino rats, and the retinae of older albino rats often showed signs of degeneration, such GFA expression was most likely pathological. Neurofilament protein-positive processes were first detectable at embryonic day 15 1/2 in the inner regions of the retina, and corresponded to the axons of retinal ganglion cells. Such processes were equivalently displayed with antibodies to 68 K [kilodaltons] and 145 K protein, but were negative with 200 K protein. Some 68 K and 145 K positive fibers could also be decorated with vimentin antibody at this stage, though at later stages this was not the case. At later development stages more 68 K and 145 K neurofilament positive processes appeared, and after the 1st postnatal wk progressively more of such processes became in addition 200 K positive, so that almost all neurofilament positive fibers in the adult stained for all 3 proteins. Such fibers, in the mature retina, corresponded to 68 K and 145 K positive optic nerve fibers, and the processes of neurones in the inner plexiform layer. All fibers in the mature optic nerve fiber layer, but not all of those in the inner plexiform layer, were stainable with 200 K antibodies. At 4 days post-natal 68K and 145 K protein positive profiles were detected in the outer regions of the developing retina, the prospective outer plexiform layer. Such profiles were always in addition vimentin positive, but negative for 200 K protein. During further development, such profiles became ordered into a well defined layer and from about postnatal day 13 all of them began to acquire 200 K protein. They could be identified as the processes of horizontal cells. They continued to express vimentin in addition to the 3 triplet proteins in the adult, a so far unprecedented situation. Neurofilament staining was detected in the mature retina only in the above described regions, the inner and outer nuclear layer and the photoreceptor processes being completely free of staining.